1. Field of the Invention
The present invention generally relates to a method of forming an ultra-thin SiN film by plasma CVD.
2. Description of the Related Art
SiN film is used widely in semiconductor processes as a gate insulation film, inter-layer wiring insulation film or surface protection film (passivation). Although SiN film is also expected to prevent diffusion of metal, etc., in the manufacturing of semiconductor devices using copper wires, the film thickness must be adjusted to an ultra-thin level of several nanometers (order of 10−9 m) in these applications in order to reduce the effective dielectric constant.
One traditional method that may be employed when an ultra-thin SiN film is used is to treat the surface of a SiO film using plasma containing nitrogen and thereby nitride the film surface (examples of this method are found in Japanese Patent Laid-open Nos. 2003-258257, 2003-188276 and 2002-009169). However, this method has the drawback of causing an increase in the number of steps. Also, under conventional methods to deposit a silicon nitride film the film deposition time needed to deposit a film of several nanometers in thickness becomes too short because the film deposition speed is too high. As a result, it is difficult to control the thickness of formed film by means of controlling the film deposition time.